The overall objective is to describe the biological interactions between the host and the bacterial flora resident in plaque and in the gingival crevice, since these are responsible for the inflammatory process and subsequent tissue destruction and bone loss. In addition to studies in man, several in vitro systems and monkey model system will be used. These will, taken as a group, allow development of a precise description of the dynamic changes in tissue permeability, of the role of immunologic reactions and mediators, and of the mechanisms for bone destruction.